Photoperiod signals are the primary regulators of reproduction in seasonally breeding animals. Melatonin is known as the hormone of darkness as its production by the pineal gland is confined to the night-time hours; thus it acts as a decoder of seasonal day length in seasonally breeding animals. Light inhibits melatonin synthesis. As days get longer in the spring, the duration of melatonin production is reduced and this lifts the inhibitory action of this hormone in a mare's reproductive activity. Horses, as long-day breeders, normally foal between May and October. However, the universal birthday for many horse breeds is January 1st. This necessitates a demand for early foals in order to produce mature yearlings and two year old racehorses to meet industry timelines for sales and racing schedules. Therefore advanced onset of the mare's breeding season is required.
Exposure of Thoroughbred breeding mares to lengthened hours of light beginning on December 1st and continuing for at least 8-10 weeks is standard industry practice in order to advance the reproductively active period of the mare's circa-annual reproductive cycle, thus permitting breeding from February 15th, the official start of the Thoroughbred breeding season. The maintenance of groups of mares indoors under lights during winter months is labour and energy intensive. Mares must remain indoors and require maintenance in terms of feeding, bedding and labour associated with their upkeep during this time. This comes at a high cost. The estimated upkeep for a mare during this time is £20/day (feed, bedding, labour, light) and if maintained for 10 weeks totals can involve costs of about £1400.
For this reason, pregnant mares are not usually maintained under lights to advance the perceived breeding season.
Multiple studies have investigated the influence of time of breeding on gestation length and found that the earlier in the year that the mare is bred, the longer the gestation period. Mares bred between January and May have on average a 10-day longer gestation period than mares bred during their natural breeding season. This has important implications for the industry as the mare has an approximate 11 month gestation period (˜330 days). Provided that she foals on time, stud managers have one month to ensure she becomes pregnant again to prevent a later foaling date the subsequent year. If the gestation length of early foaling mares could be shortened it would provide crucial extra time to permit a successful timely conception for the subsequent pregnancy. A study (Hodge et al, 1982) has shown that the administration of artificial light to pregnant mares beginning December 1st significantly shortens the gestational length by 10 days. It is assumed that this is not commonly practiced in the industry due to the high cost associated with keeping all pregnant as well as non-pregnant mares under artificial lighting.
A more recent unpublished study has shown that not only is the gestational period lengthened in early foaling mares, but that the birth weight of foals born in January and February is significantly lower than for a foal born later in the year. The Hodge (1982) study showed a tendency towards higher birth weights in mares provided with artificial lighting. It is therefore desirable to reduce gestation length and increase foal birth weight in pregnant mares.
Currently, the only known solution is to leave the stable lighting on over housed mares. The literature (Palmer and Driancourt, 1981) states that a 100 Watt light bulb in a 12 ft×12 ft stall (enough light to read a newspaper) burning for 16 hrs a day provides sufficient light for this purpose. As stated, this is costly.
U.S. Pat. No. 4,858,609 discloses a bright light mask system for shining a high intensity light into a subject's eyes at pre-selected time periods to modify circadian rhythms. The system includes a mask adapted to be worn by the subject (possibly a race horse) for covering the subject's eyes regardless of body position. The mask includes at least one light admitting aperture that is transparent to light energy. A light source is coupled to the aperture for generating and directing light into the subject's eyes. At least 2000 lux of light having a wavelength in the range of 500 to 600 nanometers (nm) is delivered to each of the subject's eyes. A controller dictates the intensity of the light generated and the periods during which the light is on.
It is an object of the present invention to provide a more cost-effective apparatus and method for inhibiting melatonin synthesis in a horse.